The introduction of aramid fibers having great tensile strength has made possible a number of applications for lightweight, high strength cables or ropes, particularly in the area of underwater cables and arrays. The strength members in such cables have traditionally been of steel which has provided the desired strength but at a considerable cost in weight. Recent studies using ropes of aramid fibers have shown that such ropes, which are very lightweight as compared with steel wire ropes of equivalent tensile strength, have applications for which steel cannot be used because of its weight but where aramid filament ropes may be used.
As compared with steel, however, such aramid cables or ropes which are marketed under the name Kevlar (a trademark of duPont Corporation) have certain properties requiring special handling. While steel wire ropes have a yield point after which they will stretch significantly before they break, Kevlar has no such yield point. Thus a conventional wire rope, when stretched close to its tensile limit, may experience overloading past the yield point on some strands, but these strands simply stretch somewhat and continue to carry their share of the load. Aramid fibers have no such characteristic, however, and tend to retain their length right up to the breaking point. Because of this, it has been difficult to provide satisfactory terminations for such aramid cables or ropes since any significant variation in strand length causes the load to be carried on the shortest strand until it breaks, then the next shortest, etc., with each strand failing under load until all are broken. Consequently, the weakest part of such a rope has usually been at the termination or just at the point where the rope or cable enters the termination. Frequently such failures occur at loadings which are no more than 60- 70% of the known strength of the cable or rope.